package com.yushi.code.common.core.utils;

/**
 * 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
 *
 * @author
 * @create
 **/
public class SnowFlakeUtil {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 10; // 序列号占用的位数
    private final static long MACHINE_BIT = 3;   // 机器标识占用的位数
    private final static long DATACENTER_BIT = 3;// 数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  // 数据中心
    private long machineId;     // 机器标识
    private long sequence = 0L; // 序列号
    private long lastStmp = -1L;// 上一次时间戳


    public static SnowFlakeUtil InitId(long datacenterId, long machineId) {
        return new SnowFlakeUtil(datacenterId, machineId);
    }

    private SnowFlakeUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {
            // 相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            // 同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            // 不同毫秒内，序列号置为0
            // sequence = 0L;
            // 单数毫秒为1，双数毫秒为0
            sequence = currStmp % 2 == 0 ? 0L : 1L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT // 时间戳部分
                | datacenterId << DATACENTER_LEFT       // 数据中心部分
                | machineId << MACHINE_LEFT             // 机器标识部分
                | sequence;                             // 序列号部分
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }

    public static Long getId() {
        return SnowFlakeUtil.InitId(1, 1).nextId();
    }

    public static String getStrId() {
        return Long.toString(getId());
    }
}
